In radio frequency signal generation and processing the reduction and suppression of noise is always a pertinent factor. In seeking to measure very low levels of intelligent signals, surrounding noise levels must be identified so that they can be reduced. Thus noise becomes the signal of interest in discrimination systems that determine noise levels that are ultimately to be removed or suppressed in signal processing. In related U.S. Pat. Nos. 4,002,970 and 4,002,971 issued to Ashley, Rast, and Barley, the present inventors, transmission line discrimination is disclosed in detail. In measuring frequency modulation noise on a continuous wave signal, the carrier signal is nulled in a discriminator section of the system. Subsequently, incidental amplitude modulation is rejected from the desired test signal and dynamic range of measurement is enhanced. In these patents, the use of an optimized transmission line discriminator circuit is set forth which allows measurement of the near carrier frequency modulation at microwave frequencies. Reference and signal channels of information are established for a signal under test. Routine calibration sequences are set forth for calibrating the systems. Additional background and prior art in the use of frequency discrimination to measure near carrier frequency modulation noise of a microwave signal is set forth in these patents and in the prior art references cited therein.